It is taking engineers longer than expected to put the finishing touches on the James Webb Space Telescope, the successor to the Hubble Space Telescope, prompting NASA to delay the launch of its next-generation observatory by five months.

NASA officials said Monday that Webb, the successor to the Hubble Space Telescope, has passed the last of...

NASA officials said they delayed the launch, long scheduled for October 2018, after realizing that it will take more time than scheduled to integrate various elements of the telescope and test them to ensure they will survive the trauma of launching into space.

“Webb’s spacecraft and sunshield are larger and more complex than most spacecraft,” said Eric Smith, the telescope’s program director at NASA headquarters in Washington, D.C. “Considering the investment NASA has made, and the good performance to date, we want to proceed very systematically through these tests to be ready for a Spring 2019 launch.”

The rescheduling is the first major shift in planning for the telescope since 2011, when a new road map replaced one that culminated in an impossible and over-budget 2014 launch. The telescope has been in planning since the 1990s, and contracts to design and build it were awarded in 2002, with an eye originally toward a 2010 launch.

NASA officials said the change will not add to the project’s $8.7 billion budget.

Thomas Zurbuchen, associate administrator for NASA’s science division, said the delay “is not indicative of hardware or technical performance concerns.”

The $8.7 billion successor to the Hubble Space Telescope is being exposed to intense vibrations as part of testing to ensure it will survive a launch...

Testing of the telescope itself and a suite of science instruments is going smoothly and on schedule at NASA’s Johnson Space Center in Houston, but integration of the bus that will hold the spacecraft and the tennis court-sized sun shield to will protect the telescope has been delayed, officials said.

The telescope is designed to see farther into space than Hubble, and with greater sensitivity to light, observing in the infrared instead of just visible light.